Minimally invasive surgery has become increasingly prevalent in spinal surgeries to correct a variety of spinal irregularities and injuries. Traditionally, surgeons relied upon “open” surgical techniques to access different areas of the spine. “Open” surgical techniques require a single, long incision along a patient's skin adjacent the spine followed by retraction of muscles and tissues to expose the surgical field. Minimally invasive surgery, on the other hand, utilizes a number of smaller incisions to provide access to the spine with tools being inserted through the incisions to perform the surgery. As a result, minimally invasive procedures often produce smaller scars, less tissue damage, and reduced recovery times. However, one problem with minimally invasive surgery is that the smaller incisions limit a surgeon's view of the surgical field. This requires the surgeon to rely to a greater extent on tactile feedback from surgical tools during surgery.
One application of minimally invasive surgery that has gained widespread acceptance is in spinal fusion procedures. As used herein, the term fusion refers to the joining of materials, such as bone or graft material, and the fusion site is the entire region in which fusion may be desired. Trauma or disease may cause instability in the spine that generates painful contact between spinal structures and elements of the nervous system. One method of correcting the instability is to secure a spinal rod near the problem area to fuse nearby vertebrae together and restore alignment of the vertebrae within the spinal column. Typically, screws are inserted into the pedicles of the target vertebrae before being secured to the spinal rod to fix the vertebrae relative to each other.
Because the pedicle is a relatively narrow structure of the vertebra, it is important that a hole drilled into the pedicle be centrally aligned along the pedicle. Misalignment of the pedicle screw produces a weakened connection between pedicle screw and the pedicle bone. Moreover, deviation from the pedicle axis during pilot hole drilling or insertion of the pedicle screw may puncture the vertebral cortex and damage adjacent nerve roots or the spinal cord.
Numerous techniques exist to aid a surgeon during installation of the pedicle screw when the surgical field is obstructed, such as during minimally invasive surgeries. One common approach relies upon the electrically conductive properties of the nervous system to measure the proximity of medical instruments to nerves by using an electrical signal. In use, the patient is placed under anesthesia and connected to an electromyograph (EMG) machine to monitor muscle contractions. The connection with the EMG machine typically comprises a collection of electrodes placed on a patient's skin. The electrodes are positioned to monitor major muscle groups connected to the nerve roots adjacent the surgical site. Because the patient is under anesthesia, the muscles being monitored should not normally contract. However, if the muscles are stimulated by an electrical signal and contract, the EMG machine will generate an audio or visual signal to warn the surgeon of the unexpected muscular activity.
The surgeon then connects an electrical signal generator such as from the EMG machine to a metallic tool, such as a drill or an awl, to be used during surgery. The signal generator energizes the tool so that when the tool is brought into proximity with a nerve root, electrical current will flow into the nerve root and cause the muscles associated with the nerve root be stimulated to contract. The EMG machine senses the muscle activity and provides an auditory and visual signal to alert the surgeon of the proximity of the tool to the nerve root. In this manner, the process supplements the surgeon's tactile feedback during surgery and reduces the likelihood of contacting nerves with the energized tool.
For example, when a surgeon uses this procedure to drill a pilot hole for a pedicle screw, there is typically no electrical communication between the energized tool and the adjacent nerve roots due to the insulating characteristics of bone. However, if the drill breaches the vertebral cortex, the electrical current directed through the drill shaft reaches the adjacent nerve root. The electrical current then travels along the nerve and causes the associated muscle to contract. At this point, the EMG machine would observe the muscle contraction and provide auditory and visual notification to the surgeon that the pedicle has been compromised. At this point, the surgeon will likely select a different installation location. Accordingly, this procedure improves the precision of pedicle screw installations even when the surgeon cannot directly view the surgical site.
For electrically connecting the EMG machine to the rotatable tool shaft, an electrical lead extending from the machine is attached at its free end to the shaft by an electrically conductive clip, such as an alligator-type clip. However, the clip is substantially fixed onto the tool shaft. Thus, when the surgeon rotates the tool shaft, the clip rotates therewith causing the wire to wrap around the rotating shaft. Such wire wrapping entangles the wire on the shaft and, depending on the amount of play in the electrical lead between the EMG machine and the tool shaft, may inhibit rotation of the shaft as well as potentially breaking the electrical connection between the machine and tool shaft.
Accordingly, there is a need for an improved connector between nerve monitoring equipment and a variety of rotatable tools used during surgery.